Thameslink is a fifty-station main-line route in the British railway system running 225 km (Template:Convert/mi) north to south through London from Bedford to Brighton, serving both London Gatwick Airport and London Luton Airport. It opened as a through service in 1988 and by 1998 was severely overcrowded, carrying more than 28,000 passengers in the morning peak. The Thameslink programme is a major £5.5 billion scheme to extend the service to a further 100 stations and to greatly increase capacity on the central London section to accommodate more frequent and longer trains. Some parts of this scheme, now well under way, will be in place by the 2012 Olympics. Thameslink services will be complemented by Crossrail, which will offer east-to-west mainline services across London.

Trains operating the "main line" service (Bedford to Brighton) include first-class accommodation. Those serving the "suburban loop" are generally standard-class-only. The previous franchisee designated these services as "Thameslink CityFlier" and "Thameslink Metro" respectively, but the present operator has dropped this branding.

Passenger services operated across London through the Snow Hill Tunnel from mid-Victorian times until World War 1, from when services terminated at Moorgate from the Midland line to the north, and at Holborn Viaduct for SE&C trains from the south, at a time when most inner cross-London traffic had been lost to buses and trams. There were separate lower-level platforms under the main part of Holborn Viaduct station known as the Snow Hill platforms, and these can still be seen today when leaving City Thameslink station travelling northwards.

The route remained operational for cross-London freight trains until 1970, just lasting into the diesel era, when the short section between Farringdon and Holborn Viaduct was closed.

The Snow Hill tunnel was re-opened to passenger trains after 72 years, allowing mainline passenger services to begin on the full Thameslink network in May 1988.[2]
On 29 January 1990 the section between Blackfriars and Farringdon was temporarily closed to permit the construction of a new alignment. The old route carrying the line through the site of the long-closed Ludgate Hill station and over the Ludgate Hill road was abandoned and immediatey demolished. The route carrying the railway under Ludgate Hill was opened on 29 May 1990 concurrently with the opening of City Thameslink station, which was initially called St. Paul's Thameslink but was renamed in 1991 to avoid confusion with St. Paul's station on the London Underground (Central Line), about Template:Convert/m away.

Around 1994 the second branch was cut back to West Croydon as this route crossed the commuter networks of what were to become several different rail companies and the onset of rail privatisation made the route increasingly difficult to maintain.

Then around 1995 a major overhaul occurred when the route was changed completely. Thameslink no longer served the West Croydon route and instead a new route to Sutton was opened up over existing track through Mitcham Junction with the line then continuing on a loop up to Wimbledon and then rejoining itself south of Streatham. It should be noted, however, that morning peak trains only run in a clockwise direction around this loop, which is a major source of inconvenience for commuters in this area.[citation needed]

By late 1998, more than 28,000 passengers were carried at morning peak times.[3]

From 1 April 2006 the franchise was taken over by First Capital Connect along with other services previously operated by WAGN.[4] The branding of most trains, stations, and signs has been changed to match the name of the new company, but City Thameslink and West Hampstead Thameslink stations keep the word Thameslink in their names as it refers to the route itself.[5] After criticism of the loss of the apt name for this group of routes, First Capital Connect's publicity now calls this set of services its "Thameslink route" to distinguish it from the former WAGN services which the company also operates.

The Moorgate branch closed permanently in March 2009 when major work on the Thameslink programme started along with various other changes.[6]

Following the success of the original scheme, plans were drawn up by successive railway authorities to upgrade the Thameslink network to cope with increasing passenger numbers which in recent years have led to severe peak-time overcrowding.[7] Network Rail obtained planning permission and legal powers in 2006,[8] funding was secured in July 2007[9] and construction began in October 2007.[10] Much of the work is due for completion by the end of 2011 with further work programmed for the period from 2012 to 2015.[11]

The Thameslink rolling stock is mainly the entire fleet of 86 Class 319 trains built by BREL between 1987 and 1990. These are electrically powered dual-voltage four-car units rated to carry 289, 308 or 319 passengers. They use 25 kV AC overhead power north of Farringdon and 750 V DC third rail to the south. Four Class 319 trains had been transferred from Southern in December 2008 and the last four followed in March 2009, from which point all 86 Class 319 trains were available for use on Thameslink.

First Capital Connect acquired 23 new-build four-coach Class 377 trains during 2009, on sublease from Southern, to be used on the Thameslink route for additional capacity and also to allow some of the Class 319 trains to be released for use on the Catford Loop service to Sevenoaks which is now jointly operated with Southeastern under Key Output 0 of the Thameslink Programme.[12]

Class 317 units built in the early 1980s were still in use when services into Moorgate (25 kV AC) ceased in March 2009 under the Thameslink Programme. The last timetabled service using a Class 317 unit ran from Farringdon to Bedford on 9 October 2009.

New energy-efficient trains will provide an additional 14,500 seats on the Thameslink route and will be delivered from 2012 to 2015.[13]

↑This service was colloquially known as the Bedpan Line from the contracted names of the terminal stations, as had happened with the Bakerloo line. In general, limited-stop trains served St Pancras, and all-station services terminated at Moorgate.